1. Field of the Invention
The present invention relates to an automotive alternator in which a voltage is generated in a stator by rotation of a rotor.
2. Description of the Related Art
FIG. 9 is a cross-section of a conventional automotive alternator, and FIG. 10 is a perspective view of the rotor in FIG. 9.
This automotive alternator includes: a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2; a shaft 6 disposed in the case 3, a pulley 4 being secured to a first end of the shaft 6; a Lundell-type rotor 7 secured to the shaft 6; fans 5 secured to both ends of the rotor 7; a stator 8 secured to an inner wall of the case 3; slip rings 9 secured to a second end of the shaft 6 for supplying electric current to the rotor 7; a pair of brushes 10 moving in contact with the surface of the slip rings 9; a brush holder 11 accommodating the brushes 10; a rectifier 12 in electrical contact with the stator 8 for converting alternating current generated in the stator 8 into direct current; and a regulator 18 fitted over the brush holder 11 for adjusting the magnitude of the alternating current generated in the stator 8.
The rotor 7 includes: a field coil 13 generating magnetic flux on passage of electric current; and a pole core 14 disposed so as to cover the field coil 13 in which magnetic poles are produced by the magnetic flux generated by the field coil 13. The pole core 14 includes a first pole core body 21 and a second pole core body 22 which are mutually interlocked. The first pole core body 21 and the second pole core body 22 are made of iron, and have tapered claw-shaped magnetic poles 23 and 24, respectively.
FIG. 11 is a perspective of the stator 8 in FIG. 9, FIG. 12 is a perspective of the stator core 15 in FIG. 9, and FIG. 13 is a partial plan of the stator core 15.
The stator 8 includes: a stator core 15 laminated from a number of steel plates through which a rotating magnetic field from the field coil 13 passes; and a three-phase stator coil 16 through which generated electric current flows. The stator core 15 includes: an annular core back 82; and a number of teeth 81 spaced evenly in the circumferential direction and extending radially inwards from the core back 82. The three-phase stator coil 16 is housed in slots 83 between adjacent teeth 81. The teeth 81 include: broad end portions 85 extending in a circumferential direction of the stator 8; and column portions 86 connecting the end portions 85 to the core backs 82. Spaces called openings 84 are formed between the end portions 85 of adjacent teeth 81.
FIG. 14 is a circuit diagram for a conventional automotive alternator of the above construction, the stator coil 16 being composed of three windings Y in a three-phase Y-connection. The rectifier 12 includes diodes 123 and 125.
In an automotive alternator of the above construction, a current is supplied by a battery (not shown) through the brushes 10 and slip rings 9 to the field coil 13, whereby a magnetic flux is generated, giving rise to a magnetic field. At the same time, the pulley 4 is driven by an engine and the rotor 7 is rotated by the shaft 6 such the stator core 15 is subjected to a rotating magnetic field, electromotive force is generated in the stator coil 16, and output current is generated by an external load connected to the automotive alternator. The alternating current generated by the stator 8 is converted into a direct current by the rectifier 12. Moreover, the current flowing through the field coil 13 is controlled by the regulator 18 to adjust the magnitude of the voltage of the alternating current generated by the stator 8.
In an automotive alternator of the above construction, there are twelve poles in the rotor 7, and thirty-six slots 83 in the stator core 15, making one slot 83 per pole per phase, and one problem has been when the dimensions of the openings 84 are reduced in order to reduce the magnetic resistance of an air gap between the stator 8 and the rotor 7, claw-shaped magnetic poles 23 and 24 overlap the end portions 85 of the same tooth 81 simultaneously when viewed from a radial direction, increasing the amount of ineffective magnetic flux flowing in the end portions 85 as indicated by arrow B and reducing the amount of magnetic flux generated by the field coil 13 being routed through the stator coil 16, thereby reducing output.